Polyester based flexible polyurethane foams, are well known articles of commerce and are conventionally prepared by reacting polyesters with organic polyisocyanates in the presence of controlled amounts of water. Typical of such foams are those prepared from (a) polyesters derived, for instance, from the interaction of a glycol, such as diethylene glycol, and adipic acid or other dicarboxylic acid, sometimes in the presence of a low molecular weight cross-linking polyol containing at least 3 hydroxy groups, such as glycerol or trimethylol propane, (b) a polyisocyanate, usually a diisocyanate, such as tolylene diisocyanate, and (c) a small amount of water, the reaction being carried out in the presence of coupling agents or emulsifiers and catalysts.
In U.S. Pat. No. 3,079,350, granted Feb. 26, 1963, to C. Bernstein, there is disclosed improvements in flexible polyurethane foams wherein polyester resins derived from mixed glycols provide highly hydrophilic foams. Such flexible urethane foams generally require a high degree of cross-linking to increase the polyester viscosity to the range necessary for providing the desired foam quality but at the expense of reducing the stress-strain properties. This patent is incorporated herein by reference.
In U.S. Pat. No. 3,298,974, granted Jan. 17, 1967, and U.S. Pat. No. 3,399,154, granted Aug. 27, 1968, to C. Bernstein, et al., there is disclosed the manufacture of rigid (i.e., not flexible) polyurethanes wherein 0 to 100% of the total dicarboxylic acid in the polyester can be replaced with phthalic anhydride.
In U.S. Pat. No. 3,769,245, granted Oct. 30, 1973, to Stewart, et al., there is disclosed the formulation of thermoplastic linear polyurethanes wherein linear hydroxyl terminated polymers, such as polyalkylene oxides, are added as part of the prepolymer.
While such prior art polyurethanes were generally useful for their specific purposes, it was desired to provide flexible polyester polyurethane foams which would be readily processable and yet exhibit improved cell structure and physical properties over the prior art polyurethanes.
It is therefore an object of the present invention to provide improved flexible polyester polyurethane foams and improved polyester resins for making same.
It is a further object of the present invention to provide non-hydrophilic polyester polyurethane foams.
It is another object of the present invention to provide polyester polyurethane foams over a wide range of densities.
It is still a further object of the present invention to provide a flexible polyurethane foam having improved stress-strain properties, good machine processing character, cellular control, structure and integrity.